FIG. 8 is a view showing a structure of a conventional antenna apparatus using a reflector antenna. In the drawing, reference numeral 10 denotes a reflector antenna part, and the reflector antenna part 10 includes a spherical main reflector 1, a secondary reflector 2, and a horn antenna 3.
Reference numeral 100 denotes a substantially cylindrical 180° polarizer, and the 180° polarizer 100 is rotatably supported by a rotary joint 110. The 180° polarizer 100 is rotated to coincide with a polarization coming from a satellite (not shown) or a polarization transmitted to the satellite, the plane of polarization is rotated, and transmission-reception is performed.
Incidentally, reference numeral 20 denotes an orthomode transducer (OMT: ORTHO MODE TRANSDUCER), and the orthomode transducer 20 divides a linear polarization signal, which is received by the reflector antenna part 10 and is transmitted through the 180° polarizer 100, into orthogonally polarizations to extract a Vertical polarization signal and an Horizontal polarization signal, or combines a V polarized and an Horizontal polarization signals orthogonal to each other and inputted from a Vertical polarization port and an Horizontal polarization port to convert them into a linear polarization signal.
The conventional antenna apparatus shown in FIG. 8 uses the 180° polarizer 100 constructed of a waveguide, there is a problem that the size of the apparatus becomes large, and is not suitable for mounting on an aircraft or the like in which an installation space is limited.
Besides, for example, JP-A-2002-141849 discloses a moving body satellite communication apparatus including an active phased array antenna which transmits a radio frequency signal outputted from a modulator-demodulator to a satellite, and receives a radio frequency signal transmitted from the satellite to output to the modulator-demodulator, a power detector for detecting the power of a reverse polarization contained in the radio frequency signal received by the active phased array antenna, and control means for controlling the plane of polarization of the active phased array antenna on the basis of the power detected by the power detector.
With respect to the transmission side active phased array antenna (transmission APAA), there are indicated a first splitter for dividing a modulating signal, which is frequency-converted by a transmission frequency converter, by the number of element antennas, a second splitter for dividing a modulating signal, which is terminated by a termination, by the number of the element antennas, and transmission APAA modules the number of which is sufficient to satisfy the antenna performance, and which receive the two-channel modulating signals of the modulating signal divided by the first splitter and the modulating signal divided by the second splitter to perform a transmission processing.
Besides, it is disclosed that each of the transmission APAA modules includes a first 90° phase combiner (90° HYB, also simply called a hybrid) for phase combining the two-channel modulating signals divided by the first splitter and the second splitter, a first and a second variable phase shifters respectively for phase shifting the two-channel modulating signals outputted from the first 90° phase combiner, first and second power amplifiers respectively for amplifying the outputs of the first and the second variable phase shifters, and a second 90° phase combiner for phase combining the output signals of the first and the second power amplifiers.
An apparatus in which the variable phase shifters as stated above and the two 90° phase combiners (hybrids) are used, and the power amounts of two inputted polarized signals are distributed at an arbitrary ratio and are outputted by changing the phase amounts of the variable phase shifters, is generally called a variable power divider.
Incidentally, a reception side active phased array antenna (reception APAA) has a similar structure to the transmission side active phased array antenna (transmission APAA) although the flow of signals to be processed is opposite.
Besides, JP-A-2-274004 discloses an array antenna including plural element antennas arranged on a curved surface and for transmitting or receiving a linearly polarized electric wave, a variable phase shifter connected to each of the element antennas, a variable power divider for distributing power amounts of two inputted polarized signals at an arbitrary ratio by changing the phase amount of the variable phase shifter, and a polarization control circuit for performing a control so that the direction of the linearly polarization of each of the elements is changed at intervals of 360°/2n (n is a positive integer).
The foregoing antenna apparatus disclosed in JP-A-2002-141849 or JP-A-2-274004 can be miniaturized as compared with the foregoing antenna apparatus using the 180° polarizer constructed of the waveguide.
However, since it is necessary that according to the required antenna performance, the many element antennas (array antennas) are arranged and the variable power divider corresponding to each of the element antennas is provided, although a highly efficient antenna apparatus can be obtained, there is a problem that it becomes expensive.
The invention has been made to solve the problems as stated above, and has an object to provide an antenna apparatus which performs transmission/reception of a signal to/from a satellite by using a reflector antenna, is suitable for mounting on an aircraft or the like, is miniaturized and is inexpensive.